摘要
晶粒尺寸对低强度材料疲劳裂纹扩展的影响规律,业已清楚,但为数不多有关高强度钢的类似工作,却出现矛盾结果。本文使用不同晶粒尺寸和经不同温度回火,即具有不同强度水平的65Mn 钢试样,进行疲劳裂纹扩展试验。研究结果表明,随奥氏体晶粒粗化,两种强度水平试样,都具有降低 dα/dN,增加△K_(th)的相同规律,且△K_(th)、△K_T 与d^(1/2)存在线性关系,但高强度试样对晶粒尺寸影响的敏感性比低强度材料低。作者通过对循环塑性区尺寸 r_y^c 的估算,分析了组织因素尺寸■的含义,并指出马氏体对奥氏体的分割作用降低了■值。高温回火使马氏体界面消失,恢复奥氏体晶界的主导作用,是不同强度材料在晶粒尺寸影响敏感性差别的主要原因。
The grain size effect on FCG is cleared for low strength materials, but it is contradictory for only a few research results of high strength steels in the same aspect.In the present paper investigated on FCG of 65Mn steel with different grain size and tempering temperature.The results show that there are same tendency for both of low and high strength levels,that is,the da/dN is decreased and ΔK_(th) is increased as austenite grain size is coarsened. There is alinear relation between ΔK_(th) ΔK_T and ■but the sensitivity of grain size effeet for the high strength steel is lower than that for low strength steel. Authors calculate the size of cyclic plastic zone r_y^c,and analyze the meaning of strength parameter l,and point out that the austenite partitioned by mar- tensite,which decreases the ■ value,and the disappearance of the martensite interface at high temperature temperiug is the reason of the sensitivity diff- erence for the two different strength level specimens.
关键词
晶粒尺寸
65MN钢
疲劳裂纹扩展
grain size
crack growth rate
crack growth threshold
cyclic plastic zone
